Estrogenic therapies include two main areas, fertility control and estrogenic replacement.
Fertility has been controlled by use of a number of orally administered hormone products. The products are ordinarily a combination of an estrogen and a progestin. A synthetic estrogen is ordinarily used as the estrogen component since the natural estrogen, 17-beta-estradiol, is almost completely destroyed, usually by over 90 percent, when taken orally. It is destroyed to a degree in the digestive tract before it is absorbed but primarily the destructive metabolism of 17-beta-estradiol occurs during the first pass hepatic metabolism. Since such a large amount is destroyed, in order to provide an effective dosage orally, a large excess must be administered with uncertain effectiveness and a large amount of unwanted metabolic products. Therefore, a synthetic estrogen such as ethinyl estradiol normally is orally administered with less than desired results.
The progestin component generally inhibits, as intended, ovulation. Also, in the case of administered progestin, a substantial amount of metabolic breakdown occurs causing undesired metabolic products with undesired effects.
Therefore, in the oral administration of what is commonly referred to as "the pill" or other orally administered products, considerably overdosing is necessary to obtain a high degree of assurance that the desired fertility control will be obtained.
A number of major side effects have reportedly been associated with the administration of oral fertility control preparations, such as thrombophlebitis and thrombosis, pulmonary embolism, coronary thrombosis, myocardial infarction, cerebral thrombosis, cerebral hemorrhage and hypertension. These side effects have been attributed to the estrogen component in the oral preparations. Use of the progestin-only preparations (mini-pill) has been found to eliminate the side effects of estrogen. However, the fertility control is less than that of the combined preparations and the menstrual cycle also becomes more irregular. It has been reported that less incidence of irregular bleeding is observed if the progestin is administered at a more constant rate of delivery. Besides the side effects, the oral fertility control preparations also have the disadvantage of fertility control efficacy depending highly on the degree of patient compliance. The risk of pregnancy is known to increase with each pill missed.
An ideal and patient-acceptable fertility control system should provide the following advantages: minimized side effect, increased ease of administration, rapid termination of treatment, if needed, and improved patient compliance. In recent years, considerable attention has already been directed to the development of implantable, intrauterine, intracervical or intravaginal fertility control delivery systems to provide a prolonged and controlled administration of steroidal hormones to the body for achieving fertility control; however, none of the delivery systems developed so far can be considered as ideal and side effect-free.
Other fertility control means have been used, such as topical creams and intravaginal devices, which deliver combinations of one or more progestins and one or more estrogens, including the naturally-occurring estrogen, 17-beta-estradiol. However, the undersirable aspects of such fertility control systems are evident.
It is, therefore, highly desired that transdermal systems be provided which permit (1) use of the natural estrogen, 17-beta-estradiol, if desired, (2) use of a minimum number of dosage units for each menstrual cycle, such as use of three successive weekly dosage units, and (3) adherence to the skin of the subject which would administer sufficiently high levels of estrogen and progestin hormones to provide high assurance of fertility control without a high amount of undesired metabolic or chemical degradative products. Development of a rate-control transdermal drug delivery system, which is capable of minimizing any individual variability and regional differences in skin permeability, is a necessity to attain a predictable blood level of a drug. The transdermal rate-control drug administration is known to offer several potential advantages for systemic medication: (i) avoidance of the risk and inconvenience of intravenous therapy and of the variability in absorption and metabolism associated with oral therapy; (ii) continuity of drug administration, permitting the use of a pharmacologically-active agent with short biological half-life; (iii) efficacy can be achieved with lower total daily dosage of drug, because of reduced hepatic first-pass metabolism and continuous drug input; (iv) less chance of over- or under-dosing, as a result of prolonged, programmed delivery of drug at required therapeutic rate; (v) provision of a simplified medication regimen; and (vi) ability to rapidly terminate the drug infusion, if needed, by removal of the drug delivery system from skin surface. Therefore, a transdermal contraceptive delivery system, which is capable of providing on a fast effective basis dual-delivery of an estrogen and a progestin at controlled rates for a specific duration would be an ideal system for achieving fertility regulation in women.
The second main area of estrogenic therapy concerns the need for estradiol replacement therapy. It is caused by menopause (the cessation of ovarian function), oophorectomy (loss of one or both ovaries by surgery) or by pituitary failure. Replacement estrogenic therapy is an important need. Besides the need to alleviate the menopausal symptoms caused by estrogenic steroid deficiency, there are additional contributions of such replacement estrogenic therapy associated with osteoporosis (loss of bone mass) and atherosclerosis. It has been found advantageous to administer also an amount of progestin as a part of such estrogenic replacement therapy. There is clearly a need for improvements in means and methods for estrogenic steroid therapy. Even though it has been found that estradiol itself or estradiol in the form of certain derivatives such as nonoor diesters (e.g., acetate esters) can be absorbed transdermally, it is desired that improved transdermal estradiol and other estrogenic steroid absorption dosage unit forms and processes of transdermal administration be developed.